1. Field of the Invention
This invention relates to a process for preparing thermoplastic elastomer laminates and more particularly to processes for preparing soft thermoplastic elastomer laminates having a thin thermoplastic elastomer foamed layer, the laminates being useful for applications as outer skin materials in automotive internal trim parts, such as instrument panels and interior sheets, and in outer skin materials for the air bag.
2. Description of the Prior Art
Thermoplastic elastomers have been widely used heretofore as outer skin materials for automotive internal trim and parts, for example, instrument panels and interior sheets. The thermoplastic elastomers possess properties such as both thermoplasticity and elasticity, and can be formed by injection molding, extrusion molding or the like into molded articles having excellent heat resistance, tensile properties, weatherability, flexibility and elasticity.
As specific examples of the thermoplastic elastomers mentioned above, there are disclosed, for example, in Japanese Patent Publn. No. 34210/1978, thermoplastic elastomers obtained by dynamically partially curing a mixture comprising 60-80 parts by weight of a monoolefin copolymer rubber and 40-20 parts by weight of a polyolefin resin. Further, Japanese Patent Publn. No. 21021/1978 discloses thermoplastic elastomers comprising (a) partially crosslinked copolymer rubber containing ethylene/propylene/non-conjugated polyene copolymer rubber having a gel content of from 30-90% by weight, and (b) a polyolefin resin. Furthermore, Japanese Patent Publn. No. 18448/1980 discloses thermoplastic elastomers obtained by dynamically cross-linking an ethylene/propylene copolymer and a polyolefin resin, either partially or completely.
Sheets of the above-mentioned thermoplastic elastomers have heretofore been used as outer skin materials for automotive internal trim and parts such as instrument panels and interior sheets, after being bonded to or fusion intergrated with core materials, such as acrylonitrile/butadiene/styrene (ABS), polypropylene, aluminum and iron.
However, such sheets of the thermoplastic elastomers as mentioned above were found to be poor in softness to the touch as outer skins.
With a view to solving the above-mentioned problem, such sheets of the thermoplastic elastomers used as outer skin materials were laminated on the back thereof with a polyethylene foam, polypropylene foam or urethane foam so that the cellular body will act as a pad, thereby imparting a soft touch to the sheets.
However, molded articles of foam backed thermoplastic elastomer sheets obtained by fabrication, such as by a vacuum forming technique, were lacking in sharpness of the shape and ridge thereof, though the polyethylene, polypropylene or urethane foam having an expansion coefficient as large as 10-30 times was capable of imparting a soft touch to the thermoplastic elastomer sheets used as outer skin materials. In addition thereto, these foams, as mentioned above, are relatively expensive.